.web-nav{
    height: inherit;
    background: linear-gradient(to bottom right, #50a3a2, #53e3a6);
}

.bg-bubbles {
    position: absolute; /*使气泡背景充满整个屏幕； */
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    /* 如果元素内容超出给定的宽度和高度，overflow 属性可以确定是否显示滚动条等行为；*/
    overflow: hidden;
    z-index:-10;
}

.bg-bubbles li {
    position: absolute;
    /*bottom 的设置是为了营造出气泡从页面底部冒出的效果；*/
    bottom: -160px;
    /* 默认的气泡大小；*/
    width: 40px;
    height: 40px;
    background-color: rgba(255, 255, 255, 0.15);
    list-style: none;
    /*使用自定义动画使气泡渐现、上升和翻滚；*/
    animation: square 15s infinite;
    transition-timing-function: linear;
    border-radius: 50%;

}
/* 分别设置每个气泡不同的位置、大小、透明度和速度，以显得有层次感；*/
.bg-bubbles li:nth-child(1) {
    left: 10%;
}

.bg-bubbles li:nth-child(2) {
    left: 20%;
    width: 90px;
    height: 90px;
    animation-delay: 2s;
    animation-duration: 7s;
}

.bg-bubbles li:nth-child(3) {
    left: 25%;
    animation-delay: 4s;
}

.bg-bubbles li:nth-child(4) {
    left: 40%;
    width: 60px;
    height: 60px;
    animation-duration: 8s;
    background-color: rgba(255, 255, 255, 0.3);
}

.bg-bubbles li:nth-child(5) {
    left: 70%;
}

.bg-bubbles li:nth-child(6) {
    left: 80%;
    width: 120px;
    height: 120px;
    animation-delay: 3s;
    background-color: rgba(255, 255, 255, 0.2);
}

.bg-bubbles li:nth-child(7) {
    left: 32%;
    width: 160px;
    height: 160px;
    animation-delay: 2s;
}

.bg-bubbles li:nth-child(8) {
    left: 55%;
    width: 20px;
    height: 20px;
    animation-delay: 4s;
    animation-duration: 15s;
}

.bg-bubbles li:nth-child(9) {
    left: 25%;
    width: 10px;
    height: 10px;
    animation-delay: 2s;
    animation-duration: 12s;
    background-color: rgba(255, 255, 255, 0.3);
}

.bg-bubbles li:nth-child(10) {
    left: 85%;
    width: 160px;
    height: 160px;
    animation-delay: 5s;
}

/* 自定义 square 动画；*/
@keyframes square {
    0% {
        opacity: 0.5;
        transform: translateY(0px) rotate(45deg);
    }
    25% {
        opacity: 0.75;
        transform: translateY(-400px) rotate(90deg);
    }
    50% {
        opacity: 1;
        transform: translateY(-600px) rotate(135deg);
    }
    100% {
        opacity: 0;
        transform: translateY(-1000px) rotate(180deg);
    }
}
